[ot] Decibels and the ear (was: Re: [plug] Hot and bothered CPU hankers for cool breeze)

[Cameron Patrick]

On Tue, Dec 16, 2003 at 09:50:21PM +0800, James Devenish wrote:
| In message <20031216124328.GA8482 at erdos.home>
| on Tue, Dec 16, 2003 at 08:43:28PM +0800, Cameron Patrick wrote:
| > On Tue, Dec 16, 2003 at 08:40:54PM +0800, Derek Fountain wrote:
| > | I'm intrigued! Why do 400 boxes not sound 400 times louder than 1 box?
| > My understanding is that a 10dB increase corresponds to ~2x louder,
| 
| Hmm...are we talking about intesity or power? In the case of intensity,
| ~3dB corresponds to 2x more intense and 10dB corresponds to 10x more
| intense. (Power presumably involves the square of intensity, so it would
| be typical to calculate 20log(f(P)), as opposed to 10log(f(I)).)

Yup, that pretty much matches with my understanding.  I /think/ I was
talking about intensity, but I'm pretty hazy now about which is which.
Intensity is change in pressure over area, right??  Something over area,
anyway.

| Of course, talking about power might be more practical since it
| relates readily to energy. But I think "louder" would be a perceptual
| phenomenon and we'd have to ask the audiologists.

Okay, I was pretty sure I remembered from year 12 physics (which I
understand I've done a lot more recently that you...) a rule of thumb
saying that 10dB intensity increase corresponds to a 2x increase in
perceived volume.  OTOH the Physics textbook that year was dodgy (e.g.
it had Copyright G Taylor, Carine SHS printed on every page!) and my
memory may well be even dodgier...  I would dig that book out but I'm
not sure where (or if!) I kept it.  Certainly I was left was the
impression that human hearing was vaguely logarithmic (hence the
prevalence of decibels when measuring sound pressure levels).

Cameron.